1. Field of the Invention
The present invention relates to a glass crack prevention laminate using a liquid crystal display optical film such as a polarizing plate, and a liquid crystal display method and device (LCD) using the glass crack prevention laminate.
2. Description of the Related Art
In a liquid crystal display according to the background art, it is essential from its image forming system that polarizing elements are disposed on opposite sides of a glass substrate which forms an outermost surface of a liquid crystal panel. Generally, a polarizing film (polarizing plate) is bonded to each surface of the liquid crystal panel.
Besides the polarizing film, various optical elements are used on each surface of the liquid crystal panel in order to improve display quality of the display. For example, a phase retarder film for preventing coloring and a luminance enhancement film for improving the viewing angle of the liquid crystal display are used. These films are generically called “optical films”.
To bond such an optical film to a surface of a liquid crystal panel, an adhesive agent is generally used. Generally, the adhesive agent is provided on a surface of an optical film to prepare an adhesive agent-including optical film. The adhesive agent-including optical film is bonded to a surface of the liquid crystal panel because it has an advantage that the optical film can be instantaneously fixed to the outermost surface of the liquid crystal panel without necessity of any drying process for fixing the optical film.
The adhesive agent needs to have performance such as stress relaxation characteristic and removability to prevent any disadvantage caused by the adhesive agent in a durability test due to heating, moistening, etc. The stress relaxation characteristic is required so that optical irregularity can be prevented from being caused by change in size of the optical film. The removability is required so that the optical film can be removed from the surface of the liquid crystal panel when the optical film is bonded to a mistaken place of the surface of the liquid crystal panel or when an alien substance is lodged between the optical film and the liquid crystal panel.
To satisfy this requirement, an optical member capable of being removed and recycled (see Patent Document 1) and an adhesive sheet having removability and stress relaxation characteristic for preventing color unevenness (see Patent Document 2) have been proposed. In addition, a liquid crystal display device using an adhesive resin interposed between a liquid crystal panel and a transparent protective plate has been proposed as a device excellent in visibility (see Patent Document 3). In these proposals, there is no particular description about impact resistance and reliability.
On the other hand, an image display device (PDP, LCD) formed in such a manner that a display panel and a protective panel are closely bonded to each other through at least one layer of a transparent adhesive agent (see Patent Document 4). In this proposal, there is neither specific description about the LCD display device nor particular description about reliability of a liquid crystal optical film though there is description about excellence in impact resistance.
[Patent Document 1] JP-A-2000-9937
[Patent Document 2] JP-A-2000-109771
[Patent Document 3] JP-A-6-75213
[Patent Document 4] JP-A-2003-29644
In the aforementioned proposals, there is no description on crack prevention of the glass substrate of the liquid crystal panel. The glass substrate is easily cracked by impact power (0.5 J) produced when a steel ball having a diameter of 50 mm and a weight of about 500 g is dropped down from a height of 10 cm or by like impact power produced by a pendulum or spring impact hammer. For this reason, there is a problem that leakage of liquid crystal makes display defective.
As described above, various kinds of adhesive agent-including optical films have been heretofore proposed. In the proposals, there is description that the optical film has impact resistance to prevent the panel from cracking at 0.5 J, and that the optical film can be bonded to the panel without any void between the optical film and the panel. The various kinds of adhesive agent-including optical films are however still insufficient in reliability.